Encoders for various types of media, such as a magnetic card, a check or a passport, are well known in the art. Universal encoders are apparatus which have a sufficiently wide slot to accept media of different thicknesses. For magnetically encoded media, encoder apparatus includes a write head which extends into the slot from one wall of the apparatus which defines the slot. The head is engaged by the advancing medium and is pushed back into the wall from which it extends. Thus, the width of the slot is adjusted to accommodate the different media.
For encoders of this type, a relatively thin medium frequently is inserted so that the bottom edge of the medium is adjacent to one wall of the slot rather than in the middle of the slot. In such instances, the medium will tilt out of a plane parallel to the slot walls. A check, for example, moving along a slot at an angle tilted with respect to the walls of the slot frequently causes incorrect data to be encoded. The reason for this is that the write head in such an encoder opposes a timing wheel which a moving medium engages. The timing wheel adjusts the encoding of data with respect to the speed at which the medium moves. This speed adjustment is necessary because the position of the data on the medium is critical to ensure proper debiting during a commercial transaction in which the medium is used.
The timing wheel has a specified vertical dimension to provide sufficient friction for the moving medium to ensure that the wheel tracks the medium. If the medium tilts, the medium is not aligned with the surface of the timing wheel, engaging instead only the top or bottom surface of the wheel. Accordingly, the wheel is not moved to track the speed of the medium and any data encoded on the medium is not done so with any reliable timing reference.